[llvm] [AMDGPU] Add doc updates for kernarg preloading (PR #67516)

[Stanislav Mekhanoshin via llvm-commits]

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@@ -4375,12 +4375,18 @@ The fields used by CP for code objects before V3 also match those specified in
                                                      dynamically sized stack.
                                                      This is only set in code
                                                      object v5 and later.
-     463:460 1 bit                                   Reserved, must be 0.
-     464     1 bit   RESERVED_464                    Deprecated, must be 0.
-     467:465 3 bits                                  Reserved, must be 0.
-     468     1 bit   RESERVED_468                    Deprecated, must be 0.
-     469:471 3 bits                                  Reserved, must be 0.
-     511:472 5 bytes                                 Reserved, must be 0.
+     463:460 4 bits                                  Reserved, must be 0.
+     470:464 7 bits  KERNARG_PRELOAD_SPEC_LENGTH     The number of dwords from
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rampitec wrote:

Add info which ASICs support this, otherwise reserved and must me 0.

https://github.com/llvm/llvm-project/pull/67516